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esaj

Interest in Charge Doctor-like device?

Interest on a Charge Doctor-like device?  

32 members have voted

  1. 1. Are you interested in getting a Charge Doctor -like device?

    • Yes, if the price is same or lower than current Charge Doctor (around 25-30€/$)
      16
    • Yes, if the price is same or slightly above the current Charge Doctor (say, <35-40€/$)
      10
    • Yes, and willing to pay more if there are more/better features than current Charge Doctor (~50+€/$)
      12
    • Yes, and willing to pay more if there's a mobile app for monitoring charging (>50€/$)
      11
    • I could donate MONEY to the cause if the device was Open Source Hardware / Software
      9
    • I could donate SOFTWARE/HARDWARE DESIGN to the cause if the device was Open Source Hardware / Software
      2
    • No, I don't feel I need to monitor my charging
      6


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Looking forward to supporting this project however I can. As a user, would love the ability to connect even more chargers in parallel as well as drive more current, at least 10A if possible. 

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10 hours ago, Seba said:

I was thinking about nRF52 as this SoC family offers integrated BLE transceiver and BLE stack that is free to use without any licensing fees. I have used this family in several designs and I have good experiences.

Do you have any recommendations or ideas on the high voltage step-down? Seems that above 100V the "simpler" solutions get scarce... I earlier found this: https://eu.mouser.com/datasheet/2/277/mp9488_r1.0-1384072.pdf  (MP9488, 450Vin max / 300mA max step-down regulator, non-synchronous), and it was "only" 2.17€ <10pcs, 1.75€ 10-99 pieces (without VAT), but, it's out of stock now and the minimum order quantity is 2500 pieces (for <1€ per piece, but I'll never have need for that many in my lifetime, and the total price would still be something like closer to 3000€ with VAT :D), and the lower quantity option has vanished from the catalog, so maybe they will only sell higher quantities in the future. Out of stock on Digikey also, minimum order quantity 100 pieces.

The next options I found so far would be either LTC3639 (150Vin max / 100mA, synchronous) or LTC3638 (140Vin max / 250mA, non-synchronous), but the price goes up a lot (over 7€ + VAT per piece for either when buying <10). There are some cheaper controllers for flyback-topologies, but I've never designed a flyback-converter (one SEPIC though, which is pretty close, but was a bitch to get my head around), and suspect that the transformer / coupled inductor would make it as "expensive".

The 0.96" OLED-displays should pull about 30mA if all pixels are lit, and I've used 20mA as a "conservative" value for the SoC (it should use less, but better leave some headroom + other components will draw some current too), the datasheet for nRF52811 ( https://www.nordicsemi.com/-/media/DocLib/Other/Product_Spec/nRF52811PSv10pdf.pdf , chapter 5.2.1) seems to only give typical values, not maximums. So 50mA or more for everything to leave headroom.

Another option would be simply not to support the 24S wheels (slightly over 100V), as there are more options if the input voltage maximum is 100V (usually the next step seems to be 80V max, which is already too low for 20S). For low currents, something like TL783 could work (linear regulator, 125V max), but it's still going to heat up considerably even with efficient cooling (dropping directly to 3.3V from 101V even with 50mA of current -> almost 5W of power dissipation!). 

 

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1 hour ago, esaj said:

Do you have any recommendations or ideas on the high voltage step-down? Seems that above 100V the "simpler" solutions get scarce... I earlier found this: https://eu.mouser.com/datasheet/2/277/mp9488_r1.0-1384072.pdf  (MP9488, 450Vin max / 300mA max step-down regulator, non-synchronous), and it was "only" 2.17€ <10pcs, 1.75€ 10-99 pieces (without VAT),

What do you think about https://www.monolithicpower.com/en/documentview/productdocument/index/doc_url/L20vcC9tcDE3NV9yMS4wLnBkZg/prod_id/Mjc5Mg/

Don't know why they list them at mouser.com for Vout = 85-305V, as in the datasheet they have examples for Vout = 18V.

... And this is listed as AC/DC converter (Ac/Dc High Voltage converters from monolithic power: https://www.monolithicpower.com/en/products/ac-dc-power-conversion/hv-buck-regulators-lt-10w.html). I would not see any substantial difference to the MP9488 - the AC/DC converters from this list just have a diode at the input (typical application) as half wave rectifier...

...

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Posted (edited)
2 hours ago, Chriull said:

What do you think about https://www.monolithicpower.com/en/documentview/productdocument/index/doc_url/L20vcC9tcDE3NV9yMS4wLnBkZg/prod_id/Mjc5Mg/

Don't know why they list them at mouser.com for Vout = 85-305V, as in the datasheet they have examples for Vout = 18V.

... And this is listed as AC/DC converter (Ac/Dc High Voltage converters from monolithic power: https://www.monolithicpower.com/en/products/ac-dc-power-conversion/hv-buck-regulators-lt-10w.html). I would not see any substantial difference to the MP9488 - the AC/DC converters from this list just have a diode at the input (typical application) as half wave rectifier...

...

Good points, I originally dismissed the AC/DC -converters, because Mouser lists them as "85VAC minimum input", but that could be just laziness or mistake on their part. Have to take a closer look into those. Some of them may rely on the input voltage "pulsing" though (even half-wave rectified, it goes down if there's no capacitors on the input).

And at least some do have minimum input voltages to work, the LinkSwitch-TN2 family was looking promising until this:

"Adequate DC Rail Voltage – Check that the minimum DC input voltage does not fall below 70 VDC at maximum load, minimum input voltage"

Many don't talk about the minimum requirement, but most datasheets never mention powering them from anything except rectified 85-240V AC or such.

EDIT: In the end, I didn't find any AC/DC -controllers that are available in Mouser and that would work certainly also with low enough voltages. Even with the MP174 (that's non-stocked and not on order) that's marked to work down to 20VAC, the datasheet says: "Avoid a minimum DC voltage below 70V; a low DC input voltage can cause thermal issue.".

So, it looks like it's back to MP9488 (if it becomes available again at some point in low quantities), LTC3639 or LTC3638, unless someone knows any other good choices or knows a better way than DC-DC buck regulation. I was thinking of a "flying capacitor" / "step-down charge pump" - style circuit to drop the voltage before regulation to use lower voltage parts, but a project that may enter the hands of others is probably not the place to start playing around with ideas and things I'm really not familiar with  ;) 

Edited by esaj
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@esaj the schematics of the mp175 https://www.monolithicpower.com/en/ev175-s-00a.html is driven with ac, a bridge inverter and then C L C - could be as "good" as DC?

But your note seems different:

2 hours ago, esaj said:

Avoid a minimum DC voltage below 70V; a low DC input voltage can cause thermal issue

For the 174

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8 minutes ago, Chriull said:

@esaj the schematics of the mp175 https://www.monolithicpower.com/en/ev175-s-00a.html is driven with ac, a bridge inverter and then C L C - could be as "good" as DC?

But your note seems different:

For the 174

Yes, MP174 is different. Look at the manufacturer list you linked to:  https://www.monolithicpower.com/en/products/ac-dc-power-conversion/hv-buck-regulators-lt-10w.html   175 is 85V AC minimum. I didn't find a mention of minimums in its datasheets, but all the graphs start from 85V and the example circuit at the end of the datasheet shows 85~265VAC input.

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100A shunt for charging is a "bit" excessive, there seems to be a 0.01-10A version (PZEM-003). Claims 1% measurement accuracy.

If i was using an inmotion charger, they’re 84V. How much Amps would it need as a maximum?

I work with bms control systems and all that stuff but i gotta be honest, a lot of what you are saying is outta space to me! Lol 

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1 hour ago, Pete G said:

100A shunt for charging is a "bit" excessive, there seems to be a 0.01-10A version (PZEM-003). Claims 1% measurement accuracy.

If i was using an inmotion charger, they’re 84V. How much Amps would it need as a maximum?

I work with bms control systems and all that stuff but i gotta be honest, a lot of what you are saying is outta space to me! Lol 

I don't know about InMotion specifically, but most stock chargers are 2A or thereabouts. The maximum charge and discharge currents are usually rated with so-called "C-rates" ( https://batteryuniversity.com/learn/article/what_is_the_c_rate ), for most lithium-chemistries, the recommended charging rate is 0.5 (2 hour charge) or 1C (1 hour charge). Faster charging stresses the cells and drops their lifespan.

With multiple packs in parallel, more current could be used than 2A safely, for example, the 16S4P / 840Wh uses 3.5Ah cells, 4 in parallel, meaning 14 amphours. Theoretically, the paralleled packs could be charged with even up to 3.5A per pack (14A total), but the charge port, wiring and possibly components in BMS might overheat / melt at that high current, so not really recommended. For wheels with big batteries, 5A should usually still be safe. The wheels with dual-ports can maybe be charged with even higher currents safely (10A?), but better check the wire gauges and that the BMS can handle that on the charging side, to prevent damage.

 

On 7/6/2019 at 3:16 AM, who_the said:

Looking forward to supporting this project however I can. As a user, would love the ability to connect even more chargers in parallel as well as drive more current, at least 10A if possible. 

Using low-side cut-off with low Rds(on) -mosfets, this could be handled, but it again pushes the prices of the components up, but not horribly. On a quick glance, for example 120V N-channels with Rds(on) around 10milliohm can be had for about 1.50€/piece, pushing 10A through one of those would "only" dissipate about 1W, which isn't difficult to deal with (for example, PowerPAK SO-8 has 20C/W maximum junction-to-ambient, 1.2C/W maximum junction-to-case, stick it to double-sided plane and stitch with thermal vias, it shouldn't warm up hardly at all, shouldn't even need much board space?).

The downside is that the ADC-resolution is limited, so using higher current range (I was originally thinking up to 5A), some resolution is lost. But for 12-bit ADC (assuming the entire voltage range could be used, but depending on commonly available sense-resistor values and fixed gain current sense amplifier, it might not be), this would mean 10A / 4096 = 0,00244... A or about 2.5mA per bit, so not that bad  ;)  Actual accuracy will likely not be that high, although oversampling might be able to keep the resolution high. Also, the limiting factor may be the wheel wiring, charge port or BMS, as mentioned above.

If the two charger were separately connected to the device, they could be measured separately (ie. "only" 5A per channel), keeping the resolution higher, but this would make the device bigger and maybe somewhat more complex, at least more expensive, as certain parts would be duplicated. 

I'm not sure if @Seba still started to design anything, he might have his hands pretty full with other stuff. Unless he's going to do the design, I'll try to get started soon...ish, likely I'll go with one of the LTC363x buck-controllers mentioned before, at least for the time being, unfortunately they're a bit expensive (likely more than 10€ with the inductors and capacitors, possibly a diode if using the non-synchronous version). Things can always be of course changed later on as needed. There are likely parts where I'll need help, like for example I have no idea how the BT-antenna dimensions are calculated, if using a PCB-antenna, or of impedance matching if using chip-antenna, although probably there are good resources available for both, and it's not the first thing I'm going to be tackling anyway. :P 

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1 hour ago, esaj said:

I'm not sure if @Seba still started to design anything, he might have his hands pretty full with other stuff.

No, I didn't started anything. You're right - I'm recently slightly busy, but I'm considering making this design within month or two.

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@esaj I see that you are very concerned about the cost of a CD replacement. I would like to make 2 statements:

I like very much your idea of XT60 + multiple adaptors (i have several devices to charge, all with different connectors) and also several buttons to make a more user friendly device

I am very frustrated with the unavailability of CD and the lack of responsse from hobby16

For these reasons, I am very interested with this project and would be willing to pay aroud 100€ for such a device

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18 hours ago, Daniel Queron said:

@esaj I see that you are very concerned about the cost of a CD replacement. I would like to make 2 statements:

I like very much your idea of XT60 + multiple adaptors (i have several devices to charge, all with different connectors) and also several buttons to make a more user friendly device

Yeah, I figured early that fixed connectors would become an issue, seeing that many people have more than one wheel, and quite often they may have completely different connectors, even if the voltages are the same. XT60 was just used as an example to explain the idea, I don't like it because it's "too tight", yanking the connectors off from each other can get difficult, and if the other end is board mounted, in the worst case you end up ripping the connector off the board before they loosen :D  Molex might have some good candidates, for example Mini-Fit series has connectors where the connectors are locking (won't come off by accident, easier to detach than XT60) and the pins are rated up to 13A, and if need be, multiple pins could be used for both positive and negative (ground).

 

Quote

I am very frustrated with the unavailability of CD and the lack of responsse from hobby16

I don't know what's going on with hobby16, I haven't tried to contact him. Maybe he got tired of making Charge Doctors.

 

Quote

For these reasons, I am very interested with this project and would be willing to pay aroud 100€ for such a device

I'll try to keep the component costs down, but unfortunately, the "more special" components (meaning mostly the >100V switcher controller) seem to be quite pricey in low quantities, also the nRF54-SoC is about three times the price a non-BT device would need (+ it needs an antenna, but on a quick glance they're relatively cheap). Also, if the device is to end up in the hands of others, I'd rather spend more money on quality components and proper protections than "cut corners" just to keep the price down. Still can't say how much it will cost in total, as there's lots of things that are still in the air regarding the overall design, and I don't know what Seba's going to cook up, he might come up with a superior design.

I was calculating the characteristics and external component values for the LT3638 last night, and it occurred to me, that while having the "support" for up to 24S (around 101V) -wheels is a good thing, not that many people have those really, most are 84V or below. Spending a bit more board space, it would be possible to add another (cheaper, but still good) lower voltage SMPS controller to the board, so that a <100V model could be made with the same board and save a bit in the component costs. Of course only one or the other controller (<100V or the LT3638) would be installed on the board, but people who don't want to pay extra for the wider input voltage range could build it/get it slightly cheaper.

 

 

Edited by esaj
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